It is known that the peptides derived from food proteins (casein, gluten) possess opioid activities such as morphine-like narcotic, analgesic activities and may be of physiological importance.
C. Zioudrou et al have reported that peptides with opioid activity are found in pepsin hydrolysates of wheat gluten and .alpha.-casein and also the activity is demonstrated by use of the bioassays including naloxone-reversible inhibition of adenylate cyclase in homogenates of neuroblastoma X-glioma hybrid cells and of electrically stimulated contractions of the mouse vas deferens (J. Biol. Chem. vol. 254, No. 7, pp. 2446-2449, 1979).
F. R. Huebner et al have recognized the opioid activities in the fragments derived from gliadin fraction by the radioreceptor assay (Peptides, vol. 5, pp. 1139-1147, 1984).
John E. Morley et al have reported that hydrolyzed gluten prolongs intestinal transit time and this effect is reversed by concomitant administration of naloxone and also that hydrolyzed gluten produces a naloxone-reversible increase in plasma somatostatinlike activity, which may have been responsible for the delayed transit time (Gastroenterology vol. 84, No. 6, pp. 1517-1523).
These reports have suggested that opioid peptides have been detected in gluten hydrolysates, but it has not as yet proven possible to elucidate the structure and character of those peptides.
We recognized that the active peptides could not isolated from pepsin hydrolyzates of wheat gluten because of its very weak activity. The present invention results from our continuing efforts to isolate new opioid peptides with the specified structures from the gluten hydrolysates.